diff --git a/FAQ.md b/FAQ.md
index 424eb29..a8b33a9 100644
--- a/FAQ.md
+++ b/FAQ.md
@@ -47,4 +47,10 @@ Good idea is to configure [privoxy](https://wiki.archlinux.org/index.php/Privoxy
 
 i2pd socks proxy has an option to pass all non-i2p traffic to Tor socks proxy. Make sure you know what are you doing!
 
-## What is floodfill mode?
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+## What is floodfill mode?
+
+Floodfills are a special kind of routers that store leasesets of various destinations. In simpler terms, they store reachability information (gateways of inbound tunnels) for i2p sites and other services (including all peers in peer-to-peer services). They play an important role in the network.
+
+In order to become floodfill, you need to enable the mode. The consequence is that i2pd will use more network and cpu time.
+
+It is not recommended to turn on floodfill if your router is not directly reachable (aka external IP address). Also, floodfill routers should have a good uptime. So, it is better to enable it on servers.
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